1. Field of the Invention
This invention relates generally to formation fluid sampling, and more specifically to an improved reservoir fluid sampling module, the purpose of which is to bring high quality reservoir fluid samples to the surface for analysis.
2. The Related Art
The desirability of taking downhole formation fluid samples for chemical and physical analysis has long been recognized by oil companies, and such sampling has been performed by the assignee of the present invention, Schlumberger, for many years. Samples of formation fluid, also known as reservoir fluid, are typically collected as early as possible in the life of a reservoir for analysis at the surface and, more particularly, in specialized laboratories. The information that such analysis provides is vital in the planning and development of hydrocarbon reservoirs, as well as in the assessment of a reservoir's capacity and performance.
The process of wellbore sampling involves the lowering of a sampling tool, such as the MDT™ formation testing tool, owned and provided by Schlumberger, into the wellbore to collect a sample or multiple samples of formation fluid by engagement between a probe member of the sampling tool and the wall of the wellbore. The sampling tool creates a pressure differential across such engagement to induce formation fluid flow into one or more sample chambers within the sampling tool. This and similar processes are described in U.S. Pat. Nos. 4,860,581; 4,936,139 (both assigned to Schlumberger); U.S. Pat. Nos. 5,303,775; 5,377,755 (both assigned to Western Atlas); and U.S. Pat. No. 5,934,374 (assigned to Halliburton).
The desirability of housing at least one, and often a plurality, of such sample chambers, with associated valving and flow line connections, within “sample modules” is also known, and has been utilized to particular advantage in Schlumberger's MDT tool. Schlumberger currently has several types of such sample modules and sample chambers, each of which provide certain advantages for certain conditions. None of these sample module/chamber combinations, however, exhibit all the characteristics of: permitting a gas charge behind the collected sample for better pressure management of the sample; being heatable up to 400° F. at internal pressures up to 25,000 psi to promote the sample fluid components to go back into solution; being sized and certified for transportation directly from the well site to the laboratory without a need to transfer the collected sample; and being equipped to serve as a storage vessel. Nor do known sample chambers/modules sufficiently minimize the dead volume during sampling to reduce contamination of the sample by a pre-filling fluid, such as water.
To address these shortcomings, it is a principal object of the present invention to provide an apparatus and method for bringing a high quality formation fluid sample to the surface for analysis.
It is a further object of the present invention to provide a sample chamber that is safely heatable to at least 400° F. at internal pressures up to 25,000 psi at the surface.
It is a further object of the present invention to provide a sample chamber that is able to be pressurized to maintain a sample in “single phase,” meaning that as the sample cools down pressure must be maintained so that components such as gas and asphaltenes, which would normally separate out of the mixture during the pressure reduction caused by the cooling of the sample mixture, will remain in solution. Components that do not stay in solution by maintaining pressure while the sample cools, such as paraffins, can be recombined by applying heat to the chamber at the surface. It is a further object of the present invention to provide a sample chamber that is certified for transportation so that, if desired, the sample can be taken directly to a lab for analysis without the need for transferring the sample from the sample chamber at the wellsite.
It is a further object to provide a sample chamber that is adapted for use as a storage vessel, meaning the sample contents will not leak across the seals that contain the sample within the sample chamber.
It is a further object to provide a sample chamber having a volume that is adequate for proper PVT sampling, but not too large that the sample could not be transferred, if desired, into a separate transportable sample bottle, most of which are 600 cc or less in capacity.
It is a further object to provide an independent validation sample chamber, having a substantially smaller capacity than the sample chamber, that will be safer and easier to heat and recombine separated sample components on the surface for validating the quality of the sample at the well site.